distance travelled on y axis

Making a game similar to doodle jump, and i would like to make a distance system as the score, but in my app is seems to be going really slow, you have to jump like 1-2 platforms to get to 1, while in doodle jump it takes 1-2 platforms to get to something like 100 -1000 also my current system counts the distance from a point even if the player moved to the side it will add 1 point even although the ball didn't actually jumped up.

 using UnityEngine;
 using System.Collections;
 using UnityEngine.UI;
 
 public class DistanceSystem : MonoBehaviour {
 
     public float distance;
     public Transform player;
     public  Text label;
     float distanceTravelled = 0; 
     Vector3 lastPosition;
 
 
 
     void Start () {
 
         lastPosition = transform.position;
 
     }
     
     // Update is called once per frame
     void Update () {
 
 
             
         distanceTravelled += Vector3.Distance(transform.position, lastPosition); 
         lastPosition = transform.position;
         label.text = distanceTravelled.ToString ("F0");
 
         }         
 
 }